Apparatus for retrieving units from a storage system

ABSTRACT

A storage system and a load handling device for lifting and moving containers stacked in the storage system are described. The storage system includes a plurality of rails or tracks arranged in a grid pattern above the stacks of containers. The grid pattern can include a plurality of grid spaces and each stack is located within a footprint of only a single grid space. The load handling device is configured to move laterally on the rails or tracks above the stacks. The load-handling device includes a container-receiving space located above the rails or tracks in use and a lifting device arranged to lift a container from a stack into the container-receiving space. The load handling device has a footprint that, in use, occupies only a single grid space in the storage system.

FIELD OF THE INVENTION

The present invention relates to apparatus for retrieving units form astorage system. In particular, but not exclusively, the inventionrelates to robotic devices for handling storage containers or bins in astore comprising a grid of stacked units.

BACKGROUND TO THE INVENTION

Some commercial and industrial activities require systems that enablethe storage and retrieval of a large number of different products. Oneknown system for the storage and retrieval of items in multiple productlines involves arranging storage bins or containers on rows of shelvesarranged in aisles. Each bin or container holds a plurality of productsof one product type. The aisles provide access between the rows ofshelves, so that the required products can be retrieved by operatives orrobots that circulate in the aisles. It will be appreciated, however,that the need to provide aisle space to access the products means thatthe storage density of such systems is relatively low. In other words,the amount of space actually used for the storage of products isrelatively small compared to the amount of space required for thestorage system as a whole.

In an alternative approach, which offers a significant improvement instorage density, containers are stacked on top of one another and thestacks are arranged in rows. The containers are accessed from above,removing the need for aisles between the rows and allowing morecontainers to be stored in a given space.

Methods of handling containers stacked in rows have been well known fordecades. In some such systems, for example as described in U.S. Pat. No.2,701,065, freestanding stacks of containers are arranged in rows inorder to reduce the storage volume associated with storing suchcontainers while still providing access to a specific container ifrequired. Access to a given container is made possible by providingrelatively complicated hoisting mechanisms which can be used to stackcontainers and to remove given containers from stacks. The cost of suchsystems are, however, impractical in many situations and they havemainly been commercialised for the storage and handling of largeshipping containers.

The concept of using freestanding stacks of containers and providing amechanism to retrieve and store specific containers has been developedfurther, for example as described in EP 0 767 113 B (Cimcorp). Cimcorpdiscloses a mechanism for removing a plurality of stacked containersusing a robotic load handler in the form of a rectangular tube which islowered around the stack of containers, and which is configured to beable to grip a container at any level in the stack. In this way, severalcontainers can be lifted at once from a stack. The movable tube can beused to move several containers from the top of one stack to the top ofanother stack, or to move containers from a stack to an externallocation and vice versa. Such systems can be particularly useful whereall of the containers in a single stack contain the same product (knownas a single-product stack). The load handler can be used to movecontainers between single-product stacks, for example to add a pluralityof containers containing a single type of product to the store, and topick up one or more containers from two or more single-product stacks tocreate a multi-product output stack. An example of this is the pickingof vegetable crates in a central warehouse to create a multi-productorder for delivery to retail stores.

In the system described in Cimcorp, the height of the tube has to be asleast as high as the height of the largest stack of containers, so thatthat the highest stack of containers can be extracted in a singleoperation. Accordingly, when used in an enclosed space such as awarehouse, the maximum height of the stacks is restricted by the need toaccommodate the tube of the load handler. Furthermore, the system is notwell adapted for the selection of a single container from amulti-product stack.

Online retail businesses selling multiple product lines, such as onlinegrocers and supermarkets, require systems that are able to store tens oreven hundreds of thousands of different product lines. The use ofsingle-product stacks in such cases can be impractical, since a verylarge floor area would be required to accommodate all of the stacksrequired. Furthermore, it can be desirable only to store smallquantities of some items, such as perishables or infrequently-orderedgoods, making single-product stacks an inefficient solution.

Accordingly, for some applications, the use of multi-product stacks, inwhich the containers making up each stack may hold different products,is favoured in order to maximise the storage density of the system. Thestored items must remain accessible reasonably quickly and easily, sothat a plurality of different items required to fulfil a customer ordercan be picked from the storage system in an efficient way, even if someof the items required are stored in a lower level of a stack, underneathseveral other containers.

International patent application WO 98/049075A (Autostore), the contentsof which are incorporated herein by reference, describes a system inwhich multi-product stacks of containers are arranged within a framestructure. A system of this type is illustrated schematically in FIGS. 1to 4 of the accompanying drawings.

As shown in FIGS. 1 and 2, stackable containers, known as bins 10, arestacked on top of one another to form stacks 12. The stacks 12 arearranged in a grid frame structure 14 in a warehousing or manufacturingenvironment. FIG. 1 is a schematic perspective view of the framestructure 14, and FIG. 2 is a top-down view showing a stack 12 of bins10 arranged within the frame structure 14. Each bin 10 typically holds aplurality of product items (not shown), and the product items within abin 10 may be identical, or may be of different product types dependingon the application.

The frame structure 14 comprises a plurality of upright members 16 thatsupport horizontal members 18, 20. A first set of parallel horizontalmembers 18 is arranged perpendicularly to a second set of parallelhorizontal members 20 to form a plurality of horizontal grid structuressupported by the upright members 16. The members 16, 18, 20 aretypically manufactured from metal. The bins 10 are stacked between themembers 16, 18, 20 of the frame structure 14, so that the framestructure 14 guards against horizontal movement of the stacks 12 of bins10, and guides vertical movement of the bins 10.

The top level of the frame structure 14 includes rails 22 arranged in agrid pattern across the top of the stacks 12. Referring additionally toFIGS. 3 and 4, the rails 22 support a plurality of robotic load handlingdevices 30. A first set 22 a of parallel rails 22 guide movement of theload handling devices 30 in a first direction (X) across the top of theframe structure 14, and a second set 22 b of parallel rails 22, arrangedperpendicular to the first set 22 a, guide movement of the load handlingdevices 30 in a second direction (Y), perpendicular to the firstdirection. In this way, the rails 22 allow movement of the load handlingdevices 30 laterally in two dimensions in the horizontal X-Y plane, sothat a load handling device 30 can be moved into position above any ofthe stacks 12.

The load handling devices 30 are further described in Norwegian patentnumber 317366, the contents of which are incorporated herein byreference. FIGS. 3A and 3B are schematic perspective views of a loadhandling device 30 from the rear and front, respectively, and FIG. 3C isa schematic front perspective view of a load handling device 30 liftinga bin 10.

Each load handling device 30 comprises a vehicle 32 which is arranged totravel in the X and Y directions on the rails 22 of the frame structure14, above the stacks 12. A first set of wheels 34, consisting of a pairof wheels 34 on the front of the vehicle 32 and a pair of wheels 34 onthe back of the vehicle 32, is arranged to engage with two adjacentrails of the first set 22 a of rails 22. Similarly, a second set ofwheels 36, consisting of a pair of wheels 36 on each side of the vehicle32, is arranged to engage with two adjacent rails of the second set 22 bof rails 22. Each set of wheels 34, 36 can be lifted and lowered, sothat either the first set of wheels 34 or the second set of wheels 36 isengaged with the respective set of rails 22 a, 22 b at any one time.

When the first set of wheels 34 is engaged with the first set of rails22 a and the second set of wheels 36 is lifted clear from the rails 22,the wheels 34 can be driven, by way of a drive mechanism (not shown)housed in the vehicle 32, to move the load handling device 30 in the Xdirection. To move the load handling device 30 in the Y direction, thefirst set of wheels 34 is lifted clear of the rails 22, and the secondset of wheels 36 is lowered into engagement with the second set of rails22 b. The drive mechanism can then be used to drive the second set ofwheels 36 to achieve movement in the Y direction.

The load handling device 30 is equipped with a crane device 40. Thecrane device 40 comprises a cantilever arm 42 that extends laterallyfrom the top of the vehicle 32. A gripper plate 44 is suspended from thecantilever arm 42 by four cables 46. The cables 46 are connected to awinding mechanism (not shown) housed within the vehicle 32. The cables46 can be spooled in or out from the cantilever arm 42, so that theposition of the gripper plate 44 with respect to the vehicle 32 can beadjusted in the Z direction.

The gripper plate 44 is adapted to engage with the top of a bin 10. Forexample, the gripper plate 44 may include pins (not shown) that matewith corresponding holes (not shown) in the rim that forms the topsurface of the bin 10, and sliding clips (not shown) that are engageablewith the rim to grip the bin 10. The clips are driven to engage with thebin 10 by a suitable drive mechanism housed within the gripper plate 44,which is powered and controlled by signals carried through the cables 46themselves or through a separate control cable (not shown).

To remove a bin 10 from the top of a stack 12, the load handling device30 is moved as necessary in the X and Y directions so that the gripperplate 44 is positioned above the stack 12. The gripper plate 44 is thenlowered vertically in the Z direction to engage with the bin 10 on thetop of the stack 12, as shown in FIG. 3C. The gripper plate 44 grips thebin 10, and is then pulled upwards on the cables 46, with the bin 10attached. At the top of its vertical travel, the bin 10 is accommodatedbeneath the cantilever arm 42 and is held above the level of the rails22. In this way, the load handling device 30 can be moved to a differentposition in the X-Y plane, carrying the bin 10 along with it, totransport the bin 10 to another location. The cables 46 are long enoughto allow the load handling device 30 to retrieve and place bins from anylevel of a stack 12, including the floor level. The vehicle 32 issufficiently heavy to counterbalance the weight of the bin 10 and toremain stable during the lifting process. The weight of the vehicle 32may be comprised in part of batteries that are used to power the drivemechanism for the wheels 34, 36.

As shown in FIG. 4, a plurality of identical load handling devices 30are provided, so that each load handling device 30 can operatesimultaneously to increase the throughput of the system. The systemillustrated in FIG. 4 includes two specific locations, known as ports24, at which bins 10 can be transferred into or out of the system. Anadditional conveyor system (not shown) is associated with each port 24,so that bins 10 transported to a port 24 by a load handling device 30can be transferred to another location by the conveyor system, forexample to a picking station (not shown). Similarly, bins 10 can bemoved by the conveyor system to a port 24 from an external location, forexample to a bin-filling station (not shown), and transported to a stack12 by the load handling devices 30 to replenish the stock in the system.

Each load handling device 30 can lift and move one bin 10 at a time. Ifit is necessary to retrieve a bin 10 (“target bin”) that is not locatedon the top of a stack 12, then the overlying bins 10 (“non-target bins”)must first be moved to allow access to the target bin 10.

Each of the load handling devices 30 is under the control of a centralcomputer. Each individual bin 10 in the system is tracked, so that theappropriate bins 10 can be retrieved, transported and replaced asnecessary.

The system described with reference to FIGS. 1 to 4 has many advantagesand is suitable for a wide range of storage and retrieval operations. Inparticular, it allows very dense storage of product, and it provides avery economical way of storing a huge range of different items in thebins 10, while allowing reasonably economical access to all of the bins10 when required for picking.

For high-volume systems in which speed of operation is critical, it isimportant to maximise the performance of each of the load handingdevices, in terms of speed of operation, battery life, reliability,lifting capacity, stability and so on. It may therefore be desirable toprovide load-handling devices that offer improved performance in one ormore of these areas.

It may also be desirable to increase the number of load handling devicesin use at any one time, to allow an increase in the speed with whichitems can be retrieved from the storage system. For example, theApplicant's co-pending International Patent Application No.PCT/GB2013/051215, the content of which is incorporated herein byreference, describes a storage system in which a plurality of each oftwo different types of load handling device are provided. One type ofload handling device is adapted to lift a plurality of bins from a stackin one operation, to allow a target bin in the stack to be accessed by asingle-bin load handling device of the second type. In such cases, itmay be desirable to reduce the size of the load handling devices inorder to minimise instances in which the optimum movement path for onedevice is hindered by the presence of other devices.

It is against this background that the present invention has beendevised.

SUMMARY OF THE INVENTION

From one aspect, the present invention concerns load handling devicesfor use in storage systems comprising a grid frame containing aplurality of stacks of containers. The load handling devices arearranged above the stacks of containers and are capable of lifting acontainer from a stack and moving the container laterally to anotherlocation. Advantageously, each load handling device occupiessubstantially only a single grid space in the storage system.

Accordingly, the present invention provides a load handling device forlifting and moving containers stacked in a storage system comprising aplurality of rails or tracks arranged in a grid pattern above the stacksof containers, the grid pattern comprising a plurality of grid spacesand each stack being located within a footprint of substantially only asingle grid space, the load handling device being configured to movelaterally on the rails or tracks above the stacks, and the load-handlingdevice comprising: a container-receiving space located above the railsor tracks in use and a lifting device arranged to lift a container froma stack into the container-receiving space; wherein the load handlingdevice has a footprint that, in use, occupies substantially only asingle grid space in the storage system.

A load handling device according to an embodiment of the inventionincludes a container-receiving space into which a container can belifted. The container-receiving space is arranged beneath a vehiclemodule, in which components such as power components, controlcomponents, drive components and lifting components are housed.

In preferred embodiments of the invention, the load handling device hasan external housing that substantially encloses the container-receivingspace. The external housing preferably has the shape of a cuboid.

By arranging the bulky components of the load handling device above thecontainer-receiving space, the footprint of the load handling device isreduced compared to the cantilever designs shown in FIGS. 3A to 3C anddescribed in NO317366, in which the bulky components are housed in avehicle module disposed to one side of the container-receiving space.Advantageously, the load handling device of the invention occupies thespace above only one stack of containers in the frame, in contrast tothe cantilever design shown in FIGS. 3A to 3C which occupies the spaceabove two stacks. This means that, by virtue of the invention, theefficiency of operation of the storage system can be improved, becausethe reduced footprint allows more load handling devices to beaccommodated and reduces the likelihood of one device obstructing theoptimum path of another.

The load handling device preferably includes a set of wheels forsupporting the load handling device above the stacks. For example,lateral movement of the load handling device may be guided by railsdisposed above the frame. The rails may be arranged in a grid pattern,allowing two-dimensional movement of the load handling device in thehorizontal plane. The wheels may engage with the rails. Two sets ofwheels may be provided, with one set being arranged to engage with afirst set of rails to guide movement of the load handling device in afirst direction, and another set being arranged to engage with a secondset of rails to guide movement of the load handling device in a seconddirection.

In an embodiment of the invention, the wheels are arranged at theperiphery of the container-receiving space. The wheels may be driven byone or more motors housed in the vehicle module. Drive may betransferred from the motors in the vehicle module to the wheels by drivetransfer means disposed around the container-receiving space. Forexample, the drive transfer means may comprise a suitable arrangement ofpulleys and drive belts.

Alternatively, the wheels may include integrated motors, for examplemotors integrated within the wheel hubs. In this way, each wheel is aself-container drive unit, and drive belts are not required. Thisarrangement is advantageous as it reduces the size of the load-handlingdevice and facilitates servicing.

One or both sets of wheels may be configured to be raised and loweredwith respect to the other set of wheels. One or more wheel lift motorsor other wheel lift devices may be housed in the vehicle module for thispurpose.

The vehicle module may house a winch or crane device for lifting thecontainer into the container-receiving space. The crane device mayinclude one or more motors for lifting the container, and the or eachmotor of the crane device may be housed in the vehicle module.

The crane device may include a gripper device configured to grip acontainer from above. The gripper device may be suspended from cablesthat can be extended and retracted from the vehicle to move the gripperdevice vertically.

In another embodiment, the load handling device is equipped with alifting device arranged to lift a single container from the stack intothe container-receiving space. The lifting device may comprise a pair oflifting arms arranged on either side of the container-receiving space,in which case the lifting device may comprise a gripper device mountedbetween the ends of the arms and arranged to grip a container fromabove.

The load-handling device preferably has a centre of mass that is locatedsubstantially directly above the gripper device when the gripper deviceis lowered below the container-receiving space.

In another embodiment, the lifting device comprises rods or cablesarranged to engage with vertical channels formed in the side walls ofthe containers. The channels may be accessed by apertures in a top faceof each container. In such an arrangement, vertically-extending spacesin the storage system are not necessary.

The rods or cables may carry an anchor mechanism arranged to engagereleasably with a container. For example, the anchor mechanism maycomprise one or more laterally-extendable arms for engaging a surface ofthe container. The anchor mechanism may be operated remotely, forexample by a wire that extends through a tubular bore of the rod orcable.

A load handling device according to another embodiment of the inventioncomprises an upper part, a lower part including a container-receivingspace, and winch means for lifting a container into thecontainer-receiving space. The winch means preferably comprises a winchmotor which is housed in the upper part, above the container-receivingspace. The lower part preferably includes a wheel assembly to facilitatelateral movement of the load handling device with respect to the frame,and the upper part also includes at least one motor for driving one ormore wheels of the wheel assembly.

The lower part may comprise a frame structure for supporting the wheelsof the wheel assembly. The frame structure may be arranged around thecontainer-receiving space. For example, the container-receiving spacemay be bounded on four sides by the frame structure. One or moreelements of the frame structure may be moveable to raise and lower afirst set of the wheels with respect to a second set of the wheels,thereby to facilitate engagement of either the first set of wheels orthe second set of wheels with a first or a second set of rails ortracks, respectively. The moveable elements of the frame structure maybe driven by a motor housed in the upper part of the load handlingdevice.

The load-handling device of the invention is preferably a self-propelledrobot vehicle.

From another aspect, the invention resides in a storage systemcomprising a frame containing a plurality of stacks of containers, andone or more load handling devices as described above. Each load handlingdevice occupies substantially a single grid space, corresponding to thearea occupied by only one stack of containers.

Accordingly, the present invention provides a storage system comprising:a first set of parallel rails or tracks and a second set of parallelrails or tracks extending transverse to the first set in a substantiallyhorizontal plane to form a grid pattern comprising a plurality of gridspaces; a plurality of stacks of containers located beneath the rails,and arranged such that each stack occupies a footprint of substantiallya single grid space; a load handling device as described above andarranged to move laterally above the stacks on the rails, the loadhandling device comprising a container-receiving space located above therails and a lifting device arranged to lift a single container from astack into the container-receiving space; wherein the load handlingdevice has a footprint that occupies substantially only a single gridspace in the storage systems.

In another aspect, the invention comprises a storage system comprising aframe containing a plurality of stacks of containers, a first handlingdevice capable of lifting a plurality of containers from a stack in asingle operation, and a second handling device capable of lifting asingle container and moving the container laterally. The first andsecond handling devices are disposed above the frame and areindependently moveable to access different stacks. The second handlingdevice is of the type described above, and occupies a spacecorresponding substantially to only one stack of containers.

In this aspect, the provision of a first handling device capable oflifting a plurality of containers from a stack in a single operationalong with a second handling device capable of lifting a singlecontainer and moving the container laterally provides an optimumsolution when seeking to retrieve a container which is located in themiddle or bottom of a stack. In such a case, only two lifting operationsneed be carried out to retrieve the target container, which greatlyincreases the speed and efficiency of the retrieval process compared toprior art arrangements in which only one container can be lifted at atime.

The storage system may further comprise one or more port locations atwhich containers can be removed from and/or added to the storage system.The load handling device of the invention may be capable of transportinga target container from a stack to a port location. The containers maycomprise open-topped bins. The containers may be arranged to interlockor engage with one another in the vertical direction when formed in astack.

In a typical application, multiple handling devices may be employed sothat multiple containers can be lifted and moved simultaneously. Thehandling devices may be of different types, and may be selected tobalance the cost and energy consumption of the system with the speed andflexibility of operation. One benefit of the present invention is that,because the load handling devices occupy the space above only one stack,the efficiency of a multiple-device system can be improved compared toprior art load handling device designs which occupy two or more stackspaces. The gain in efficiency may arise from being able to accommodatemore load handling devices in a given system, from optimising therouting of the device using the space gained by the reduced devicefootprints, or from a combination of these factors.

Preferred and/or optional features of each aspect of the invention maybe used, alone or in appropriate combination in the other aspects of theinvention also.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a frame structure for housinga plurality of stacks of bins in a known storage system;

FIG. 2 is a schematic plan view of part of the frame structure of FIG.1;

FIGS. 3A and 3B are schematic perspective views, from the rear and frontrespectively, of a known load handling device for use with the framestructure of FIGS. 1 and 2, and FIG. 3C is a schematic perspective viewof the known load handling device in use lifting a bin; and

FIG. 4 is a schematic perspective view of a known storage systemcomprising a plurality of load handling devices of the type shown inFIGS. 3A, 3B and 3C, installed on the frame structure of FIGS. 1 and 2.

Embodiments of the present invention will now be described, by way ofexample only, with reference to the remainder of the accompanyingdrawings, in which like reference numerals are used for like features,and in which:

FIG. 5 is a schematic perspective view of a load handling deviceaccording to an embodiment of the invention;

FIGS. 6A and 6B are schematic perspective views of the load handlingdevice of FIG. 5 with part of the load handling device being cut-away inFIGS. 6A and 6B to show the inside of the device, and FIG. 6C shows onepossible system architecture of the device;

FIG. 7 is a schematic perspective view of a storage system comprising aplurality of known load handler devices of the type shown in FIGS. 3A,3B and 3C and a plurality of load handler devices of the type shown inFIG. 5, installed on the frame structure of FIGS. 1 and 2;

FIGS. 8, 9 and 10 are schematic side, perspective and top views of aload handling device according to another embodiment of the inventionand with the outer casing omitted;

FIG. 11 is a schematic perspective view of the load handling device ofFIGS. 8 to 10 with the outer casing omitted;

FIG. 12 is a side view of the load handling device of FIGS. 8 to 11;

FIG. 13 is a schematic perspective view of a wheel suitable for use inthe load handling device of FIGS. 8 to 12;

FIG. 14 is a schematic perspective view of part of a load handlingdevice according to another embodiment of the invention;

FIGS. 15 and 16 are schematic perspective and side views of internalcomponents of the load handling device of FIG. 14; and

FIG. 17 is a perspective view of a load handling device according to afurther embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 5 shows a load handling device 100 according to an embodiment ofthe invention. The load handling device 100 comprises a vehicle 102equipped with a winch or crane mechanism 104 to lift a storage containeror bin 106, also known as a tote, from above. The crane mechanism 104includes winch cables 108 and a grabber plate 110. The grabber plate 110is configured to grip the top of the container 106 to lift it from astack of containers 106 in a storage system of the type shown in FIGS. 1and 2.

Referring also to FIGS. 6A and 6B, the vehicle 102 comprises an upperpart 112 and a lower part 114.

The lower part 114 is fitted with two sets of wheels 116, 118, which runon rails provided at the top of the frame of the storage system. Atleast one wheel of each set 116, 118 is driven to enable movement of thevehicle 102 in X- and Y-directions respectively along the rails. As willbe explained below, one or both sets of wheels 116, 118 can be movedvertically to lift each set of wheels clear of the respective rails,thereby allowing the vehicle 102 to move in the desired direction.

The wheels 116, 118 are arranged around the periphery of a cavity orrecess 120, known as a container-receiving recess, in the lower part114. The recess 120 is sized to accommodate the bin 106 when it islifted by the crane mechanism 104, as shown in FIG. 6A. When in therecess 120, the bin 106 is lifted clear of the rails beneath, so thatthe vehicle 102 can move laterally to a different location. On reachingthe target location, for example another stack, an access point in thestorage system or a conveyor belt, the bin 106 can be lowered from therecess 120 (as shown in FIG. 6B) and released from the grabber plate110.

The upper part 112 of the vehicle 102 houses all of the significantbulky components of the load handling device, as shown in FIG. 6C. Theupper part 112 houses the battery and associated electronics,controllers and communications devices, motors for driving the wheels116, 118, motors for driving the crane mechanism 104, and other sensorsand systems.

In this way, the footprint of the vehicle 102 is larger than the size ofa bin 106 only enough to accommodate the wheels 116, 118 either side ofthe recess 120. In other words, the vehicle 102 occupies a single gridspace in the storage system. In this way, the vehicle 102 thereforetakes up the minimum possible amount of space in the X-Y plane, and hasa footprint approximately half that of the prior art cantilever designshown in FIG. 3. For comparison, FIG. 7 shows load handling devices 100according to the invention in use in a storage system of the type shownin FIGS. 1 and 2, alongside prior art cantilever-type load handlingdevices 30 of the type shown in FIG. 3. It can be seen that the priorart devices 30, although less tall, occupy two stack spaces compared tothe taller but smaller-footprint devices 100 of the invention.

The load handling devices 100 of the invention can also offer improvedstability, increased load handling capacity and reduced weight comparedto the cantilever-type prior art load handling devices 30, because inthe invention the load of the containers is suspended between the pairsof wheels on each side of the vehicle. In contrast, the prior-artdevices 30 must have a relatively heavy vehicle module to counterbalancethe load in the cantilever configuration.

FIGS. 8 to 12 show one embodiment of the invention. The upper part 112of the vehicle 102 houses three main motors: a Z-drive motor 150 used toraise and lower the winch cables 108, which are wound onto spools 109mounted on drive shafts situated at opposite sides of the vehicle 102;an X-drive motor 152 which drives the first set of wheels 116, and aY-drive motor 154 which drives the second set of wheels 118. The upperpart 112 of the vehicle also houses a battery 156 to power the motors,and controllers, sensors and other components as described above withreference to FIG. 6C.

Drive is transferred from the X- and Y-drive motors 152, 154 to therespective sets of wheels 116, 118 by means of belt drive mechanisms.The X-drive motor 152 drives a pulley 160 connected to a short driveshaft 162 that extends across the vehicle body. Drive is transferredfrom the short drive shaft 162 to each wheel in the first set of wheels116 by an X drive belt 164. The Y-drive motor 154 drives a pulley 170connected to a long drive shaft 172 that extends across the vehicle bodyin a direction perpendicular to the short drive shaft 162. Drive istransferred from the long drive shaft 172 to each wheel in the secondset of wheels 118 by a Y drive belt 174.

The belt-driven wheels 116, 118 are mounted at the bottom of the lowerpart 114 of the vehicle 102. The use of drive belts 164, 174 to transferdrive from the motors to the wheels enables the motors 152, 154 to bemounted in the upper part 112 of the vehicle.

In this embodiment, the first set of wheels 116 can be raised clear ofthe rails or lowered onto the rails by means of a wheel positioningmechanism, as shown most clearly in FIGS. 9, 11 and 12. Each wheel 116is mounted on an arm 180 that is pivotally mounted at its outer end. Aninner end of each arm 180 is connected to the lower end of a respectivelinkage 182. The upper ends of both linkages 182 are connected to thelower end of a common linkage 184. In turn, the upper end of the commonlinkage 184 is connected to a lever arm 186 that is moved by a motor188. By operating the motor 188 to draw the common linkage 184 upwards,the first set of wheels 116 can be raised so that the second set ofwheels 118 alone is engaged with the rails, allowing movement of thevehicle 102 in the Y-direction. By operating the motor 188 to push thecommon linkage 184 downwards, the first set of wheels 116 move downwardsto engage with the rails and to lift the vehicle so that the second setof wheels 118 is lifted clear of the rails, as shown in FIGS. 9, 11 and12. The vehicle 102 can then move in the X-direction.

The wheels 118 of the second set are mounted to fixed T-pieces 190disposed at either end of the lower part 114 of the vehicle 102.

FIGS. 8, 9 and 12 show the load handling device 100 with a bin 106lifted into the recess 120. FIG. 11 shows the load handling device 100with the bin 106 beneath the device 100 and the grabber plate 110 aboutto engage with the bin 106. The wheels 116, 118 and the associatedsupport pieces, linkages and drive belts 164, 174 are arranged aroundthe edges of the recess 120, so that the upper part 112 of the vehicle102 is solidly supported.

FIG. 13 shows a wheel 200 suitable for use as one of the wheels 116, 118of the load handling device 100. The wheel 200 has a toothed centralchannel 202 that forms a pulley for cooperating with a drive belt 164,174. The channel 202 is bounded by two rubber tyres 204, which bear uponthe rails in use. The wheel 200 can be mounted to an arm 180 by way ofan axle (not shown) that extends through an axial hole 206 in the wheel200. This wheel design is compact and balanced, to minimise wear, andthe tyres 204 serve to keep the drive belt 164, 174 in alignment in use.

FIG. 14 shows two wheels 200 mounted in a frame structure 210 of a loadhandling device according to another embodiment of the invention. As inthe previous embodiments, in this embodiment the load handling devicecomprises a vehicle with an upper part 112 that houses the majorcomponents of the device and a lower part having a recess 120 foraccommodating a bin, with the wheels 200 being arranged on four sides ofthe recess (the wheels on only one side are shown in FIG. 14).

In this case, the frame structure 210 comprises two parallel panels thataccommodate the wheels 200 therebetween. A drive belt 212 is provided totransfer drive to the wheels 200 from a motor housed in the upper part112 of the vehicle.

Referring additionally to FIGS. 15 and 16, the wheels 200 in thisembodiment can be raised and lowered by moving the frame structure 210relative to the upper part 112 of the vehicle. The frame structure 210is mounted to a body 230 of the upper part 112 of the vehicle by way ofrails 232. The rails 232 are fixed to the body 230 in a verticalorientation, and the frame structure 210 is slidably mounted to therails 232.

The frame structure 210 is retained by a pair of linkages 240 thatextend between the panels. The bottom ends of the linkages 240 areattached to respective shafts 242 that bridge the gap between thepanels. The top ends of the linkages 240 are rotatably attached tothreaded bosses 246 that are mounted on a threaded horizontal driveshaft244. The bosses 246 are slidably attached to horizontal rails 248.

The driveshaft 244 is driven by a motor 250 by way of a drive belt (notshown). When the driveshaft 244 is rotated in a first direction, the topends of the linkages 240 move apart to push the frame structure 210downwards, thereby to lower the wheels 200 onto a rail. When thedriveshaft 244 is rotated in a second, opposite direction, the top endsof the linkages 240 move together to pull the frame structure 210upwards, lifting the wheels 200.

Although only one frame structure 210 with two wheels 200 is shown inFIGS. 14 to 16, it will be appreciated that an identical frame structure210 would be provided on the opposite side of the vehicle. Both framestructures 210 are raised and lowered by a common motor, so the fourwheels 200 can be lifted and lowered in unison to control engagement ofthis first set of wheels 200 with rails extending in a first directionacross the frame. Although not shown in FIGS. 14 to 16, the vehicleincludes another set of wheels arranged to engage with rails extendingin a second, perpendicular direction across the frame when the first setof wheels is lifted.

It will be appreciated that many different variations and modificationsare possible. For example, both sets of wheels may be powered by asingle motor, with a suitable transfer arrangement to direct power tothe appropriate set of wheels. In other embodiments, one or more of thewheels may include an integrated motor or a motor located adjacent thewheel. An example of this is shown in FIG. 17.

Referring to FIG. 17, this shows a load-handling device 252 according toa further embodiment of the invention. The device 252 has acuboid-shaped external housing 254 to which a plurality of wheels 256are mounted near a lower edge 258 of the housing 254. The wheels 256 aremotorised hub wheels, with each wheel 256 having a motor integratedwithin a hub 260 of the wheel 256. The motors are used to drive therespective wheels 256 directly, and hence this embodiment does notrequire drive belts connected between the wheels and drive motors.

In this example the motors are powered by batteries located within sidewalls 262 of a lower part 264 of the housing 254, adjacent to acontainer-receiving space 266 of the device 252. Locating the batterieslow down in this way has the advantageous effect of lowering the centreof gravity of the device 252, thereby increasing its stability andallowing higher acceleration and deceleration. The device 252 isotherwise similar to the previous embodiments and contains similarmechanisms for raising and lowering the wheels 256, and a similarlifting device for lifting a container into the container-receivingspace 266. The batteries located in the side walls 262 are also used topower these components.

In any of the previously-described embodiments, the mechanism used tolift containers into the container-receiving space could take anysuitable form. For maximum stability and load capacity, it is desirableto provide four lifting cables, with one cable disposed near each of thecorners of the device, but a different arrangement, for example withfewer cables, could be used if desired. Conveniently, all of the cablesare spooled and unspooled using a single motor, but more than one motorcould be used if desired.

Instead of a motor, the mechanism used to lift the wheels may use linearactuators, such as linear motors or hydraulic rams. Instead of usingbattery power, other means of powering the load-handling devices will beapparent to persons skilled in the art, for example using overhead poweror by supplying power via the rails on which the devices run.

It will be appreciated that features described in relation to oneparticular embodiment are interchangeable with features described inrelation to the other embodiments. For example, the motorised hub wheelsdescribed in relation to FIG. 17 could be used on any of the otherembodiments and/or the batteries could be located low down adjacent thecontainer-receiving space in any of the embodiments to improve stabilityand increase acceleration/deceleration. Other variations andmodifications not explicitly described above will also be apparent tothe skilled reader.

The invention claimed is:
 1. A storage system comprising: a first set ofparallel rails or tracks and a second set of parallel rails or tracksextending transverse to the first set in a substantially horizontalplane to form a grid pattern including plural grid spaces; a frameworkfor defining columns beneath the plural grid spaces for retaining pluralstacks of containers located beneath the rails, and configured such thateach stack will be located within a footprint of a single grid space;and a load handling device configured to move laterally above thecolumns on the rails, the load handling device including acontainer-receiving space located above the rails and a lifting devicearranged to lift a single container from a respective column into thecontainer-receiving space; wherein the load handling device includes anexternal housing that substantially encloses the container-receivingspace; wherein the load handling device is configured to move in a firstdirection along the first set of parallel rails or tracks and in asecond direction along the second set of parallel rails or tracks;wherein the load handling device includes a wheel assembly having afirst set of wheels for engaging with the first set of parallel rails ortracks to guide movement of the device in the first direction and asecond set of wheels for engaging with the second set of parallel railsor tracks to guide movement of the device in the second direction;wherein the wheels are arranged around a periphery of thecontainer-receiving space; and wherein the external housing extends nofurther than the wheels such that the load handling device has afootprint that occupies only a single grid space in the storage system.2. A storage system according to claim 1, wherein the lifting devicecomprises: a gripper device configured to grip a container from abovethe grid spaces.
 3. A storage system according to claim 2, wherein theload handling device comprises: a lifting mechanism configured to raiseand lower the gripper device relative to the container-receiving space.4. A storage system according to claim 1, wherein each load handlingdevice comprises: means for selectively engaging and disengaging thefirst set of wheels with the first set of parallel rails; and means forselectively engaging and disengaging the second set of wheels with thesecond set of parallel rails.
 5. A load handling device, comprising: acontainer-receiving space configured to accommodate a container; anexternal housing that substantially encloses the container-receivingspace; and a wheel assembly having a first set of wheels to be engagedwith a first set of parallel rails or tracks of a storage system toguide movement of the device in a first direction and a second set ofwheels to be engaged with a second set of parallel rails or tracks ofthe storage system to guide movement of the device in a seconddirection, wherein the first and second sets of wheels are arrangedaround a periphery of the container-receiving space and on an outersurface of the housing, and wherein the external housing extends nofurther than the wheels such that the load handling device has afootprint that occupies only a single grid space in the storage system.6. A load handling device according to claim 5 in combination with astorage system, the storage system comprising: a first set of parallelrails or tracks and a second set of parallel rails or tracks extendingtransverse to the first set in a substantially horizontal plane to forma grid pattern including plural grid spaces; and a framework fordefining columns beneath the plural grid spaces for retaining pluralstacks of containers located beneath the rails, and configured such thateach stack will be located within a footprint of a single grid space. 7.The load handling device according to claim 6, comprising: a liftingdevice configured to lift a container from a stack into the containerreceiving space, wherein the load handling device is configured to movein a first direction along the first set of parallel rails or tracks andin a second direction along the second set of parallel rails or tracks,wherein the second direction is transverse to the first direction. 8.The load handling device of claim 6, wherein the housing is shapedsubstantially in a cuboid.
 9. The load handling device according toclaim 5, comprising: an upper part housing at least power components,control components, drive components and/or lifting components, and alower part including the container-receiving space, wherein the lowerpart is arranged directly beneath the upper part.